How to Calculate for Low Voltage Transformer Line Loss

A low voltage landscape lighting system can add value to your home while providing safety and beauty. When installing a low voltage lighting system, it is important to always deliver between 11 and 12 volts of electricity to the light fixtures. Extended runs of cable with multiple light fixtures can quickly lose voltage. You can avoid costly mistakes with a few calculations.

Calculator

Instructions

- 1
  Design your lighting system. Measure wire distances and determine how many lights you will put on each wire run. Calculate the number of watts of power the wire run will carry by adding the wattage of all the lights on that particular wire run. (25 watt light x 3 lights) = 75 watts total.
- 2
  Using your calculator, multiply the total wire distance of the wire run by the total watts of power being carried on the same wire run. (75 watts x 100' wire run) = 7500
- 3
  Divide the above answer by 7500. 7500 is the constant divider for low voltage outdoor lighting wire. (7500/7500) = 1. This answer is the total number of volts you will lose for that wire run.
- 4
  Subtract the above answer from the number of volts your transformer delivers. A low voltage transformer for outdoor lighting delivers 12 volts. (12-1) = 11. The lights on this particular wire run will receive 11 volts.

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